Semiconductor light-receiving device and method for manufacturing the same

ABSTRACT

Disclosed is a semiconductor light-receiving device having high reproducibility and reliability. Also disclosed is a method for manufacturing a semiconductor light-receiving device. Specifically disclosed is a semiconductor light-receiving device  100  with a mesa structure wherein a light-absorbing layer  6 , an avalanche multiplication layer  4  and an electric-field relaxation layer  5  are formed on a semiconductor substrate  2 . The light-absorbing layer  6 , avalanche multiplication layer  4  and electric-field relaxation layer  5  exposed in the side wall of the mesa structure are protected by an SiN x  film or an SiO y N z  film. The hydrogen concentration in the side wall surface of the electric-field relaxation layer  5  is set at not more than 15%, preferably not more than 10% of the carrier concentration of the electric-field relaxation layer  5.

TECHNICAL FIELD

The present invention relates to a semiconductor light-receiving deviceused in an optical communication for example and a method formanufacturing the same.

BACKGROUND ART

In recent years, as a semiconductor light-receiving device for opticalfiber communication, several types of semiconductor light-receivingdevices are proposed. Especially, a mesa structure semiconductorlight-receiving device is attracting attentions. The reason is that itcan be produced in mass by simple processes with low cost. And it couldalso reduce a parasitic capacitance in order to achieve high-speed.

FIG. 10 shows a schematic diagram of a semiconductor light-receivingdevice having a mesa structure. As shown in FIG. 10, in a semiconductorlight-receiving device 900 with a mesa structure, an n electrode 901 isprovided at the rear surface of a substrate 902, and a mesa structure isadopted at the light incident side of the substrate 902. And inside ofit, an n type cladding layer 903, absorbing layer 904 and p typecladding layer 905 are laminated. Furthermore, over the light incidentsurface of the p type cladding layer 905, a p electrode 906 is provided.As described above, for the semiconductor light-receiving device with amesa structure, as a pn junction excluding a light-absorbing unit isetched, a pad electrode capacitance on p side can be reduced. This is anadvantage as a light-receiving device used for telecommunications sectorfor high-speed response.

Moreover, as a semiconductor light-receiving device, there is anAvalanche Photo diode (APD) having a structure with a signal amplifyingfunction inside the device in light of improving sensitivity. FIG. 11shows a basic structure of a mesa APD. As shown in FIG. 11, an APD 910adopts a mesa structure on a light incident side of a substrate 912. Andan n type cladding layer 913, avalanche multiplication layer 914,electric-field relaxation layer 915, absorbing layer 916, p typecladding layer 917 and p type contact layer 918 are laminated. On asidewall of the laminated layer, a lateral protection film 919 isformed. Furthermore, to the incident surface of an input light, a pelectrode 920 is formed.

As for the absorbing layer 916, a semiconductor material capable ofsufficiently absorbing an incident light is selected. And especially forcommunication, InGaAs is adopted which maintains a high absorptioncoefficient on shorter wavelength side than the wavelength 1.60 μm. Asfor the multiplication layer 914, a wide gap material is selected whichis able to suppress a leak current even in a high electric field as itspeeds up and multiplies the injected carrier. Especially forcommunication, InAlAs or InP is adopted.

In the APD 910, an electron or positive hole (first carrier) generatedby absorbing a light in the absorbing layer 916 is accelerated by anelectric field inside the absorbing layer 916 of the APD, which isgenerated by applying a reverse bias. The first carrier is injected intothe avalanche multiplication layer 914 while holding kinetic energy andcollides with a neutral atom inside the avalanche multiplication layer914. As a result, an electron and positive hole (second carrier) aregenerated. Moreover, the first carrier and second carrier areaccelerated by the electric field and by colliding to a neutral atom, anew carrier is generated. By the process consecutively occurring, thegenerated electron and positive hole are expotentially increased, thatis, multiplied. By this, the APD is able to sense a small signal ascompared to a normal photodiode.

Considering an APD used in an optical communication band, a InGaAs layerand InAlAs multiplication layer which are lattice matched over an InPsubstrate are the basic structure. When applying a reverse bias to thepn junction, an internal electric field distribution at an operation ofthe APD is shown in FIG. 12. An electric field of each layer iscontrolled by the doping concentration distribution among themultiplication layer, electric-field layer and absorbing layer. Thevertical axis of FIG. 12 is an electric field E.

An important point to operate the APD successfully is to control each ofthe electric fields in the absorbing layer and multiplication layer. Forexample for the APD used in the abovementioned optical communicationband, an electric field of the InGaAs absorbing layer must be controlledfrom 50 to 150 kV/cm, an electric field of the multiplication layer mustbe controlled to 600 kV/cm or more. The InGaAs constituting theabsorbing layer has a narrow gap and its band gap energy is 0.75 eV.Thus in an electric field of 150 kV/cm or more, a noise caused by atunneling current is generated, causing a sensitivity deterioration.Moreover, a high electric field more than necessary is not preferable inlight of reliability. Because the electron or positive hole generated inthe absorbing layer is not accelerated enough in not more than 50 kV/cm,an energy barrier with the adjacent semiconductor layer cannot beovercome by drift running, thus a problem is generated in terms ofhigh-speed response characteristics or the like.

On the other hand in the multiplication layer, the carrier injected intothe multiplication layer is accelerated by applying a high electricfield and collides with lattice to generate a new pair ofelectron-positive hole. A signal is amplified by this process repeatedlyoccurring in the multiplication layer, however to occur the processconsecutively, an electric field of 600 kV/cm or more is required.

As in the abovementioned example, the most important thing in the APD isto control the electric fields of the avalanche multiplication layer andabsorbing layer. In order to make the APD operate properly, optimumelectric fields are required for the absorbing and multiplicationlayers. The control of the electric field distribution is performed bycontrolling the layer thickness of the electric-field relaxation layerheld between the avalanche multiplication and absorbing layer andcarrier concentration. That is, controlling the width of theelectric-field relaxation layer and carrier concentration is animportant key to the reliability and characteristics of the APD.

In order to achieve an APD having a high reliability in a conventionalmethod, a planar structure or pseudo planar structure is adopted forcontrolling the electric field using an ion implantation and diffusiontechnique or the like for the abovementioned layer structure to form apn electrode over a crystal surface (for example non-patent document 1).This method surrounds the multiplication layer, electric-fieldrelaxation layer and absorbing layer with InP implanted with Be ion soas to avoid exposing the multiplication layer portion where a highelectric field is applied. Such structure is referred to as a guard ringstructure.

Furthermore, in the APD having a planar structure, the periphery of theguard ring structure is protected with a SiN_(x) film. However for theAPD having these structures, there are problems that the manufacturingmethod is generally complicated. And it is difficult to improvecharacteristics of the device and a tolerance of manufacturingcondition.

On the other hand, as a mesa semiconductor light-receiving device, a pnstructure is formed in growth process to form a light-receiving area bya mesa etching, and an electric field distribution is distributedone-dimensionally, so the device design is easy. Thus it has advantagesof a higher degree of freedom, easier to improve device characteristicsand improve manufacturing yield as compared with the abovementionedplanar type. However a device that achieved sufficient reliability hasnot developed yet, because a high electric field is applied to theabsorbing layer and avalanche multiplication layer and in addition theselayers are exposed to the surface.

Next, characteristics of a device are considered from devicefabrication. In the mesa semiconductor light-receiving device, as shownin FIG. 11, the sidewalls of the multiplication layer 914 and fieldelectric relaxation layer 915 which are applied with a high electricfield and the absorbing layer 916 that is narrow gap and likely togenerate a tunneling current are exposed. In light of devicereliability, it is important to protect the lateral faces of theselayers.

As a conventional method, a method for obtaining a protection film witha SiN_(x) film created by a plasma CVD (Chemical Vapor Deposition)method or a method for protecting with polyimide and BCB or the like aresuggested. However in these protection films, there is a problem instability of the semiconductor and interface. Furthermore, for thepolyimide and BCB or the like, there is also a problem inhygroscopicity. Therefore, as for the APD constituted of a mesastructure, it has been difficult to achieve a high reliability of morethan million hours in an operation of the APD at 85 degrees.

In a normal mesa type photodiode, a SiN_(x) film created by a plasma CVDis used as a protection film. The abovementioned SiN_(x) protection filmis manufactured by a plasma CVD using SiH₄ and NH₃ as materials. Thismethod has extremely simple processes and is advantageous in terms ofreproducibility and process cost.

However when applying the abovementioned method to the APD, hydrogenradicals diffuse into the APD which are generated by the decompositionof the NH₃. Especially for the hydrogen diffused in the electric-fieldrelaxation layer, the hydrogen radical stably bonds with main componentsof the electric-field relaxation layer in the vicinity of an impurity,and the impurity becomes into a state not satisfactory functioning as anacceptor. And after a passivation, the carrier concentration of theelectric-field relaxation layer changes especially near the sidewall.

This increases a leak current of the side wall thus it is not apreferable method in light of device characteristics and reliability.Furthermore as described above, the carrier concentration of theelectric-field relaxation layer is a key to the reliability of the APDand if the carrier concentration changes, it brings a cause todeteriorate the reliability of the APD. However it is extremelydifficult to control the amount of diffusion of the hydrogen radicalduring the process, thus it is difficult to improve reproducibility andreliability. This has been a problem for structure and manufacture in amesa APD.

As a method for preventing the influence by the diffusion of theabovementioned hydrogen radical, as a conventional technique, there is amethod (for example non-patent document 2) for not etching themultiplication layer to remain, laminating InP doped with Fe in theetched portion (guard ring) and protecting its surface with a SiN_(x)film. Even in this method, as with the abovementioned non-patentdocument 1, the manufacturing process is extremely complicated and it isdifficult to improve device characteristics and yield.

[NON-PATENT DOCUMENT 1] Isao Watanabe, Takeshi Nakata, Masayoshi Tsuji,Kikuo Makita, Toshitaka Torikai, and Kencho Taguchi, J. LightwaveTechnol., vol. 18, p. 2200-2207, Dec. 2000. [NON-PATENT DOCUMENT 2]

S. Tanaka, S. Fujiki, T. tsuchiya, S. Tsuji, Monday Afternoon, OFC2003,vol. 1, 67

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

As described above, in a conventional method, it was not possible toprotect the sidewall of the mesa APD and create the one with highreliability and reproducibility. Furthermore in a conventional methodfor covering the lateral face of the APD with a SiN_(x) film, theinfluence of the hydrogen passivation has not been removed.

Means for Solving the Problems

According to an aspect of the present invention, there is provided asemiconductor light-receiving device having a mesa structure constitutedof a semiconductor layer including a light absorbing layer, an avalanchemultiplication layer and an electric-field relaxation layer over asemiconductor substrate includes a SiN_(x) film or a SiO_(y)N_(x) filmfor protecting lateral faces of the light absorbing layer, the avalanchemultiplication layer and the electric-field relaxation layer in the mesastructure, where a hydrogen concentration at least in a part of thelight absorbing layer, the avalanche multiplication layer andelectric-field relaxation layer is not more than 15% of a carrierconcentration in the electric-field relaxation layer. With the hydrogenconcentration within the above range, even if the carrier concentrationin the electric-field relaxation layer changes, the electric field inthe light absorbing layer and avalanche multiplication layer can bewithin a required range.

According to another aspect of the present invention, there is provideda manufacturing method of a mesa semiconductor light-receiving deviceincluding a light absorbing layer, an avalanche multiplication layer andan electric-field relaxation layer over a semiconductor substrate, themethod includes forming a mesa semiconductor structure and forming aSiN_(x) film or SiO_(y)N_(x) film using at least N₂ gas as a nitrogensource to a lateral face of the mesa semiconductor structure. Byprotecting the lateral faces of the multiplication layer andelectric-field relaxation layer which are applied with a high electricfield and the absorbing layer that is likely to generate a tunnelingcurrent and is narrow gap with the SiN_(x) film or SiO_(y)N_(x) film, adevice with high reliability can be obtained.

Especially, the manufacturing method of a semiconductor light-receivingdevice according to the present invention, in a formation process of theSiN_(x) film or SiO_(y)N_(z) film, the SiN_(x) film or SiO_(y)N_(z) filmis formed using at least N₂ gas as a nitrogen source. By using N₂ gas asa nitrogen source, it is possible to suppress from generating radicalhydrogen to minimum, thus the amount of hydrogen diffused in the APD canbe suppressed.

Furthermore, according to another aspect of the present invention, thereis provided a manufacturing method of a mesa semiconductorlight-receiving device including a light absorbing layer, an avalanchemultiplication layer and an electric-field relaxation layer over asemiconductor substrate, the method includes forming a mesasemiconductor structure, forming a SiN_(x) film or a SiO_(y)N_(z) filmand performing a heat treatment in inert gas atmosphere at 450 degreesCelsius or more and 700 degrees Celsius or less. By using the above heattreatment, the radical hydrogen included in the APD is dischargedoutside the APD and the hydrogen concentration in the APD can besuppressed.

ADVANTAGES OF THE INVENTION

According to the present invention, it is possible to provide an APDwith high reproducibility and reliability and a manufacturing method forthe APD.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram showing the structure of anavalanche light-receiving device according to the present invention;

FIG. 2 is a view for explaining a conductivity evaluation unit in anavalanche light-receiving device according to the present invention;

FIG. 3 is a graph showing an electric field strength dependency in asemiconductor light-receiving device;

FIG. 4 is a graph showing a result of a reliability evaluation test ofthe avalanche light-receiving device according to the present invention;

FIG. 5 is a cross-sectional diagram showing the structures of anembodiment 1 and embodiment 2 according to the present invention;

FIG. 6 is a view showing I-V characteristics of the avalanchelight-receiving device according to the present invention;

FIG. 7 is a graph showing a time variation of the avalanchelight-receiving device according to the present invention;

FIG. 8 is a graph showing a result of a reliability evaluation testaccording to the embodiment 2 of the present invention;

FIG. 9 is a perspective view showing a waveguiding structure of anembodiment 3 of the present invention;

FIG. 10 is a cross-sectional diagram showing the structure of aconventional semiconductor light-receiving device;

FIG. 11 is a cross-sectional diagram showing the structure of aconventional avalanche light-receiving device; and

FIG. 12 is a view showing an internal electric field of an avalanchelight-receiving device.

DESCRIPTION OF REFERENCE NUMERALS

-   1 ELECTRODE-   2 SUBSTRATE-   3 CLADDING LAYER-   4 MULTIPLICATION LAYER-   5 ELECTRIC-FIELD RELAXATION LAYER-   6 ABSORBING LAYER-   7 CLADDING LAYER-   8 CONTACT LAYER-   9 SURFACE PROTECTION FILM-   10 p ELECTRODE-   11 n ELECTRODE-   21 n ELECTRODE-   22 InP SUBSTRATE-   23 n TYPE InP CLADDING LAYER-   24 InAlAs MULTIPLICATION LAYER-   25 p TYPE InAlAs ELECTRIC-FIELD RELAXATION LAYER-   26 InGaAs ABSORBING LAYER-   27 p TYPE InP CLADDING LAYER-   28 p TYPE InP CONTACT LAYER-   29 SiN_(x) FILM OR SiO_(y)N_(z) FILM-   30 p ELECTRODE-   31 n ELECTRODE-   41 InP INSULATING SUBSTRATE-   42 n TYPE InP BUFFER LAYER-   43 n TYPE InGaAsP GUIDE LAYER-   44 InAlAs MULTIPLICATION LAYER-   45 InAlAs ELECTRIC-FIELD RELAXATION LAYER-   46 InGaAs ABSORBING LAYER-   47 p TYPE InGaAsP GUIDE LAYER-   48 p TYPE InP CLADDING LAYER-   49 p TYPE InGaAs CONTACT LAYER-   50 SiN_(x) PROTECTION FILM-   51 p ELECTRODE-   52 ANTIREFLECTIVE FILM-   53 n ELECTRODE-   54 p TYPE PAD ELECTRODE-   55 BUMP REALIZATION POLYIMIDE LAYER-   901 n ELECTRODE-   902 InP SUBSTRATE-   903 n TYPE InP GUIDE LAYER-   904 InGaAs ABSORBING LAYER-   905 p TYPE InP GUIDE LAYER-   906 p ELECTRODE-   911 n ELECTRODE-   912 SUBSTRATE-   913 n TYPE GUIDE LAYER-   914 AVALANCHE MULTIPLICATION LAYER-   915 ELECTRIC RELAXATION LAYER-   916 ABSORBING LAYER-   917 p TYPE GUIDE LAYER-   918 p ELECTRODE-   919 LATERAL PROTECTION LAYER-   920 p ELECTRODE

BEST MODES FOR CARRYING OUT THE INVENTION

The structure of a mesa APD 100 according to an embodiment 1 of thepresent invention is described hereinafter with reference to FIG. 1. Inthe structure in this embodiment, an electrode 1 having an additionalrole of a reflector is formed to a semi-insulating substrate 2. Theelectrode 1 is formed to facilitate the implementation and is formedincluding metal with high reflectivity. Furthermore, the substrate sidesurface of the electrode 1 is mirror polished, a light not absorbed inan absorbing layer 6 and transmitted is reflected at the surface of thesubstrate side of the electrode 1 and can be transmitted to theabsorbing layer 6.

Moreover, to the opposite side of the electrode 1, over the substrate 2,an n type cladding layer 3 is formed. Furthermore, a mesa structure isprovided over the n type cladding layer 3. Furthermore inside the mesastructure, an avalanche multiplication layer 4, field electricrelaxation layer 5, absorbing layer 6, cladding layer 7, p type contactlayer 8 are formed and overlapped in this order from bottom. A pelectrode 10 is formed above a part of the p type contact layer 8.Furthermore, the surface of the mesa type avalanche photodiode 100 iscovered with a SiN_(x) film or SiO_(y)N_(x) film 9. For the absorbinglayer 6, a semiconductor material having a high absorption rate of aninput light is selected. For the multiplication layer 4, in order toaccelerate the injected carrier to multiply by applying a high electricfield, a wide gap material is selected which is capable of suppressing atunneling current even in a high electric field.

The reason a part of the n type cladding layer 3 is removed here is, asshown in FIG. 2, to remove the SiN_(x) film or SiO_(y)N_(x) film 9 overthe semi-insulating InP substrate 2 and to expose the surface of thesemiconductor and to confirm the effect of the hydrogen passivation bychecking surface electric conductivity. Thus the n type cladding layer 3may exist all over the substrate 2. Moreover, the n type cladding layer3 functions as an n side contact layer. An electrode 11 is formed overthe n type cladding layer 3. In FIGS. 1 and 2, the n electrode 11 isformed over the n type cladding layer 3 but it is only an example andnot limited to this position.

The APD 100 of this embodiment protects the lateral face of theavalanche multiplication layer 4, electric-field relaxation layer 5 andlight-absorbing layer 6 with the SiN_(x) film or SiO_(y)N_(z) film 9. Bythis, it is possible to prevent from exposing the avalanchemultiplication layer 4, electric-field relaxation layer 5 and absorbinglayer 6 which are applied with a high electric field. Furthermore, atleast a part of hydrogen concentration of the avalanche multiplicationlayer 4, electric-field relaxation layer 5 and light-absorbing layer 6is suppressed to be not more than 15% of the carrier concentration dopedin the field electric relaxation layer 5.

By adopting the abovementioned hydrogen concentration, as the carrierconcentration of the electric-field relaxation layer 5 rarely changes,the electric fields of the avalanche multiplication layer 4 andlight-absorbing layer 6 can be set to appropriate values, thus an APDwith high reliability can be achieved.

When forming the SiN_(x) film or SiO_(y)N_(z) film 9, at the same timewhen a hydrogen passivation occurs in the electric-field relaxationlayer 5, a hydrogen passivation occurs in the avalanche multiplicationlayer 4 and light-absorbing layer 5. This is because that as the fieldelectric relaxation layer 5 is extremely thin, it is not possible toform the SiN_(x) film or SiO_(y)N_(z) film 9, where a hydrogenpassivation occurs, only to the lateral face of the field electricrelaxation layer 5. Therefore, as long as the part of hydrogenconcentration for either the avalanche multiplication layer 4 or lightabsorbing layer 5 is not more than 10% of the carrier concentrationdoped to the electric-field relaxation layer 5, it can be consideredthat hydrogen concentration not more than 10% of the carrierconcentration doped to the electric-field relaxation layer 5 is includedin the electric-field relaxation layer 5 at the same time.

FIG. 3 is an example of the calculation result of the dependency of thefield electric relaxation layer carrier concentration for the electricfield strength of the absorption and multiplication layers. For thisdevice, InGaAs is used for the absorbing layer and the carrierconcentration is 1×10¹⁵ cm⁻³ with a thickness of 1.0 μm. Furthermore,for the avalanche multiplication layer, InAlAs is used and the carrierconcentration is 1×10¹⁵ cm⁻³ with a thickness of 0.2 μm. For theelectric-field relaxation layer, InAlAs is used with a thickness of 0.04μm.

In the above composition, an optimum electric field strength in theabsorbing layer and avalanche multiplication layer is respectively 50 to150 kV/cm and 600 kV/cm or more. From FIG. 3, when setting a center ofthe carrier concentration in the electric-field relaxation layer to1.0×10¹⁸, it is acceptable if the amount of change in the carrierconcentration is within 15% from the center in order to keep theelectric field strength of the absorption or multiplication layer withinthe range of above optimum value. As the hydrogen radical bonds with animpurity to change the carrier concentration, the carrier concentrationmay roughly be the one subtracting the hydrogen diffusion amount fromthe impurity concentration doped to the semiconductor layer. Asdescribed above, it is important to suppress the hydrogen concentrationnot more than 15% of the impurity concentration.

More general conditions are considered. A design range of themultiplication layer electric field of the APD to manufacture is setbetween 600 to 700 kV/cm. On the other hand, when manufacturing an APDhaving such multiplication layer electric field, suppose that amanufacture tolerance of the electric field for the light absorbinglayer/electric-field relaxation layer interface is from 50 to 150 kV/cmand manufacture variation at a trial production (for example in-planedistribution) is from about 50 to 150 kV/cm. As for the manufacturevariation, for example the distribution of wafer in-plane is examined inadvance and by determining an area to have a trial production afterthat, it can be determined beforehand.

Under such trial conditions, for example if the amount of relaxation ofthe electric-field relaxation layer fluctuates during the process anddecreases by 100 kV/cm, it is expected that an electric field of theinterface has a distribution of 150 to 250 kV/cm (close to thedistribution in reality). As a result, the manufacture variation doesnot overlap with the manufacture tolerance at all.

At this time, (for the ease of calculation) suppose that real numbers ofmanufacture variation in interface electric field are distributed withequal density in the variation range, the process manufacture yield canbe calculated from the length of overlapped area between the manufacturevariation and manufacture tolerance. In the above case, as there is nooverlap between the manufacture variation and manufacture tolerance, theprocess manufacture yield is 0%.

According to such method, in a device with initial multiplication layerelectric field strength 600 to 700 kV/cm, when calculating the processmanufacture yield if a deviance in the relaxation amount of theelectric-field relaxation layer during process is generated for x%, theresult shown in table 1 can be obtained.

TABLE 1 MULTIPLICATION LAYER x % ELECTRIC FIELD 5% 10% 15% 18% 600 KV77% 50% 21% 0% 700 kV 72% 39%  0% 0%

Therefore, as a result of the calculation, if the deviance of theelectric-field relaxation layer generated during process can besuppressed to 18% or less, for a device with design multiplicationelectric field strength 600 kV/cm, a certain number of complete devicescan be obtained definitely (if making devices of large enough number).By suppressing the deviance of the electric-field relaxation layer to15% or less, for a device with design multiplication electric fieldstrength 600 to 700 kV/cm, a certain number of complete devices can beobtained definitely.

By suppressing the deviance in the electric-field relaxation layer to10% or less, for a device with design electric field strength 600 to 700kV/cm, it is possible to obtain some complete devices with highprobability of at least 39%. Furthermore, in such case, it can beexpected that even for a device with the design electric field strengthnot from 600 to 700 kV/cm, complete devices can be obtained. Moreover,by suppressing the deviance of the electric-field relaxation layerwithin 5%, for a device with design multiplication electric fieldstrength 600 to 700 kV/cm, complete devices can be obtained withextremely high probability of at least 72%.

In an actual trial production, as there are causes for yielddeterioration other than the deviance in the electric-field relaxationlayer, in order to obtain complete devices of certain number, it can beconsidered that the deviance x in the electric-field relaxation layer ata process for the device with design electric field strength 600 to 700kV/cm must be 15% or less as an essential condition.

This invention has such structural features and also has features in amanufacturing method of the structure. In an example of themanufacturing method of the semiconductor light-receiving deviceaccording to this embodiment, N₂ or SiH₄ and O₂ or N₂O which can furthersuppress the generation of the hydrogen radicals are used instead of NH₃and SiH₄ to manufacture the SiN_(x) or SiO_(y)N_(z) film by a plasma CVDfor decomposing. As N₂ has less decomposition efficiency than NH₃, thefilms are manufactured by ECR (Electron Cyclotron Resonance) methodusing a high-frequency plasma 60 MHz or 2.4 GHz. By using this method,the amount of generated hydrogen radical is suppressed and thus theeffect of hydrogen passivation can be restrained.

Furthermore, another manufacturing method of a semiconductorlight-receiving device according to this invention a heat treatment isperformed in inert gas atmosphere at 450 degrees Celsius or more andalso 470 degrees Celsius or less after manufacturing the SiN_(x) film orSiO_(y)N_(z) film at the surface of the APD using NH₃ gas, SiH₄ gas andO₂ gas or N₂O gas.

FIG. 4 shows an experimental result of a device reliability of anannealing temperature. In this test, a semiconductor light-receivingdevice is stored in a state where a reverse bias is applied to thedevice so that a current of 100 μA flows in 180 degrees N₂ atmosphere.Then in the measurement, the semiconductor light-receiving device is putat a room temperature and a dark current is measured in a voltagecorresponding to 0.9 times more than a breakdown voltage. As shown inFIG. 4, for (a) sample applied with a heat treatment, (b) sample appliedwith a heat treatment under N₂ atmosphere at 450 degrees Celsius for 10minutes, (c) sample applied with a heat treatment under N₂ atmosphere at550 degrees Celsius for 10 minutes and (d) sample applied with a heattreatment under N₂ atmosphere at 630 degrees Celsius for 10 minutes, thedark current is measured for 1000 hours.

As shown in FIG. 4, for a sample that is annealed for 10 minutes at anannealing temperature from 450 to 630 degrees Celsius, it has not beendeteriorated until 1000 hours. In a low-temperature of 450 degreesCelsius or less, the hydrogen radical is not discharged enough from thesemiconductor. As for the APD, at a passivation of the SiN_(x) film orSiO_(y)N_(z) film to the lateral face of the electric-field relaxationlayer for controlling electric field strength distribution, it isdifficult to control the electric field strength distribution becausethe radical hydrogen that is disjunct from the material of SiH₄ gasbeing diffused and an acceptor is deactivated and the carrierconcentration in the electric-field relaxation layer is changed.Moreover, conversely at a high-temperature of 700 degrees Celsius ormore, crystallinity of the semiconductor itself is broken up and a filmis peeled and broken due to a difference in expansion coefficient of theSiN_(x) film and a semiconductor or of the SiO_(y)N_(z) film and asemiconductor.

As described above, the optimum temperature is in the range from 450 to700 degrees Celsius. By performing this heat treatment, the hydrogenradical got inside the APD is discharged outside through the passivationfilm and it is considered that electric field strength of the avalanchemultiplication layer, electric-field relaxation layer and lightabsorbing layer can reach to the required range.

EMBODIMENT 1

A mesa APD 200 and a manufacturing method thereof according to theembodiment 1 of the present invention are described hereinafter withreference to FIG. 5. The semiconductor light-receiving device of theembodiment 1 is a mesa APD. By using a growing apparatus such as GS-MBE(Gas Source-Molecular Beam Epitaxy) apparatus, a laminated structure ofthe semiconductor layer as shown in FIG. 5 is formed and then anelectrode is manufactured.

As shown in FIG. 5, an n type InP cladding layer 23 is formed over asemi-insulating InP substrate 22. The n type InP cladding layer 23 isformed by doping Si as an impurity and has a film thickness of 1.0 μm.The n type InP cladding layer 23 functions as an n side contact layer.

The multiplication layer 24 is formed of an undoped InAlAs and has afilm thickness of 0.2 μm. The electric-field relaxation layer 25 isformed of a p type InAlAs and has a film thickness of 0.04 μm (carrierconcentration 1×10¹⁸ cm⁻³). The absorbing layer 26 is formed of anundoped InGaAs and has a film thickness of 1.0 μm. The cladding layer 27is formed of a p type InP layer and has a film thickness of 1.0 μm. Ap-InP with higher p concentration is formed thereabove.

After that, a mesa structure is formed with a resist as a mask. To formthe mesa structure, a wet etching or dry etching is used. After that, asa surface protection film, a SiN_(x) film or SiO_(y)N_(z) film 29 isformed with the thickness of 400 nm. To be more specific, as a sourcegas, N₂ gas or SiH₄ gas and O₂ gas is used and the source gas isdecomposed using a plasma of 60 MHz frequency to form the SiN_(x) filmor SiO_(y)N_(z) film 29. After that, a p type electrode 30 and n typeelectrode 31 are formed.

In order to confirm the effects of this embodiment, as shown in FIG. 2,the SiN_(x) film or SiO_(y)N_(z) film over the semi-insulating InPsubstrate 22 is peeled to expose the semiconductor surface and surfaceelectric conductivity is examined. The Q portion in FIG. 2 correspondsto conductivity evaluation portion. As a layer with high hydrogenconcentration is formed on the surface usually, a trap is passivated andelectric conductivity is emerged. However by using the method of thisembodiment, the electric conductivity of the substrate can besuppressed.

Furthermore, as another method to confirm the effects, when forming theSiN_(x) film or SiO_(y)N_(z) film by the method of this embodiment, aSiN_(x) film or SiO_(y)N_(z) film is formed over a p type semiconductorsubstrate (InP and GaAs or the like) at the same time. By removing theSiN_(x) film or SiO_(y)N_(z) film of the semiconductor substrate andevaluating a conductivity type of the semiconductor substrate surface,the effects of this embodiment can be confirmed.

When forming by a conventional plasma CVD method, a passivation for ptype dopant impurity is generated by an invasion of hydrogen to thesurface, and a phenomenon can be seen in which a conductivity type isreduced. For example when forming a SiN_(x) film over a semiconductorsubstrate having a p type concentration of 5×10¹⁸ cm⁻³, suppose that thedegree the hydrogen invading to the substrate surface is 2×10¹⁸ cm⁻³ andthe passivation rate is 100%, the carrier concentration of the surfaceis reduced to 3×10¹⁸ cm⁻³ . The amount of change at this time is 40%decrease in the carrier concentration. On the other hand when using themethod of this embodiment, the change for electric conductivity in topsurface can be suppressed to 15% decrease or less.

FIG. 6 is I-V characteristics of a device manufactured by theabovementioned manufacturing method of the semiconductor light-receivingdevice according to the present invention. (e) is a measurement when a 1μW of light is entered and (f) is a measurement at a condition wherelight is completely blocked. From the I-V characteristics shown in FIG.6, at 10 V, approx. 1 μA photocurrent flows and when the light isblocked, only a dark current of about hundredth part thereof flows, thusit can be seen that a favorable APD is realized.

FIG. 7 is a result of a reliability test by high-temperatureacceleration. In this test, a semiconductor light-receiving device isstored in a state where a reverse bias is applied to the device so thata current of 100 μA flows in 180 degrees Celsius N₂ atmosphere. Then inthe measurement, the semiconductor light-receiving device is put at aroom temperature and a dark current is measured in a voltagecorresponding to 0.9 times more than a breakdown voltage. (g) is adevice that has formed a SiN_(x) film by a plasma CVD (13 MHz) with NH₃and SiH₄ as material. (i) is a device that has formed a SiN_(x) film bya plasma CVD (60 MHz) with N₂ and SiH₄ as material. (j) is a device thathas formed a SiN_(x) film by a plasma CVD (60 MHz) with N₂ and SiH₄ asmaterial and then the SiN_(x) film is annealed at 550 degrees Celsiusfor 10 minutes.

The semiconductor light-receiving device of the SiN_(x) filmmanufactured by the manufacturing method using NH₃ gas is deterioratedin a few hours, while the time variation in the dark current valueconcerning the semiconductor light-receiving device manufactured usingN₂ gas as a nitrogen source is suppressed. Moreover, for thesemiconductor light-receiving device created using N₂ gas as a nitrogensource, it can be seen that the time variation in the dark current valueis further suppressed by annealing at 550 degrees Celsius. This is aneffect of using N₂ gas instead of NH₃ gas. To form SiO_(y)N_(z) film, O₂gas must be added as a material, however it does not especiallyinfluence the amount of hydrogen generation, thus the samecharacteristics can be achieved even for the SiO_(y)N_(z) film.

EMBODIMENT 2

In a semiconductor light-receiving device according to an embodiment 2,hydrogen from the electric-field relaxation layer is removed by a heattreatment. The structure is same as the embodiment 1.

As shown in FIG. 5, the n type InP cladding layer 23 is formed over theInP substrate 22. The n type InP cladding layer 23 is formed by dopingSi as an impurity and has a film thickness of 1.0 μm. The n type InPcladding layer 23 functions as an n side contact layer.

The multiplication layer 24 is formed from an undoped InAlAs and has afilm thickness of 0.2 μm. The electric-field relaxation layer 25 isformed from a p type InAlAs and has a film thickness of 0.04 μm (carrierconcentration 1×10¹⁸ cm⁻³) The absorbing layer 26 is formed from anundoped InGaAs and has a film thickness of 2.0 μm. The cladding layer 27is formed from a p type InP layer and has a film thickness of 2.0 μm. AP type contact layer 28 is formed from a p type InP layer and has a filmthickness of 0.1 μm.

After that, a mesa structure is formed with a resist as a mask. To formthe mesa structure, an etchant of HBr or H₂O₂ etc. is used. After that,as a surface protection film, a SiN_(x) film or SiO_(y)N_(z) film 29 isformed for the thickness of 400 nm with NH₃ and SiH₄ as material. Inthis process, hydrogen diffuses into the electric-field relaxation layer25 and reduces an activation rate of Be, which is an acceptor impurity.This influence causes to increase field electric strength of theabsorbing layer 26 and effects to increase a dark current andreliability for the APD 200.

In this embodiment, in order to reduce this influence, a heat treatmentis performed in a nitrogen atmosphere. The heat treatment kept 500degrees Celsius under N₂ atmosphere for 10 minutes. After that, a pelectrode 30 and n electrode 31 are formed respectively to p and nsides. The p electrode 30 is formed over the p type InP contact layer 28and n electrode 31 is formed over the n type InP cladding layer 23.After that, a high-temperature acceleration test is performed in thesame method as in the embodiment 1.

FIG. 8 shows a test result. (k) is a device not heat treated, (l) to (o)are annealed for 10 minutes and their annealing temperatures arerespectively (l) 400 degrees Celsius, (m) 450 degrees Celsius, (n) 630degrees Celsius and (o) 550 degrees Celsius. As for the sample annealedat 400 degrees Celsius, there is no effect and deterioration isgenerated soon. However for the sample annealed at 450 degrees Celsiusor more, an improvement in reliability by the annealing was confirmed.

EMBODIMENT 3

The high reliability achieving method of this invention can be appliedto a waveguide structure, which is an edge face incident type. FIG. 9shows a schematic diagram of a waveguide type device 400. Layers arelaminated in the following order over a Fe-InP substrate 41. An n typeInP buffer layer 42 for obtaining an n electrode, 0.5 μm of an n typeInGaAsP guide layer 43 with composition wavelength 1.2 μm, 0.2 μm ofInAlAs multiplication layer 44, 0.2 μm of InAlAs electric-fieldrelaxation layer 45, 0.5 μm of InGaAs absorbing layer 46, 0.5 μm of ptype InGaAsP guide layer 47 with composition wavelength 1.2 μm, 1.0 μmof p type InP cladding layer 48 and 0.2 μm of p type InGaAs contactlayer 49 are consecutively grown and formed.

After that, a light-receiving unit area is remained and the portion forforming the n electrode is etched to the n type InP buffer layer 42 andother portions are etched to the substrate 41. The mesa structure'swidth W is 10 μm on the incident side, 5 μm on the backend side and awaveguide length L is 50 μm. After that, a SiN_(x) protection film 50 isformed with N₂ and SiH₄ as source gas and an edge face is manufacturedby opening wall. Likewise to the edge face, an edge face protection filmis formed by the method indicated in this invention with N₂ and SiH₄gas. After that, a p electrode 51, antireflective film 52, n electrode53, p type pad electrode 54 and bump relaxation polyimide layer 55 areformed. In this structure, an incident light enters from the A portionshown in FIG. 7 and absorbed while guiding wave in the absorbing layer.A high quantum efficiency can be achieved even with a thin absorbinglayer and it is possible to reduce carrier transit time in the absorbinglayer. As the protection film uses the method described in thisembodiment, a high reliability can be achieved.

Furthermore, a deactivation of the impurity due to the diffusion ofhydrogen atom into a semiconductor is also generated for an n typeimpurity. Thus this embodiment is also effective to an APD constitutedof a positive hole injection type InP multiplication layer and InGaAsabsorbing layer.

It is apparent that the present invention is not limited to the aboveembodiments but it may be modified and changed without departing fromthe scope and spirit of the invention. Moreover in this embodiment, alight-receiving device constituted from III-V group semiconductor istaken as an example, however this embodiment is not limited to thelight-receiving device constituted from III-V group semiconductor but iseffective to a light-receiving device constituted from II-VI groupsemiconductor such as GaN or ZnCdSe system or IV group semiconductorsuch as Si system.

1-8. (canceled)
 9. A semiconductor light-receiving device comprising: amesa structure including a light absorbing layer, an electric-fieldrelaxation layer, and an avalanche multiplication layer; a SiN_(x) filmor a SiO_(y)N_(z) film for protecting lateral faces of the mesastructure, wherein a hydrogen concentration at least in a part of themesa structure is not more than 15% of a carrier concentration in theelectric-field relaxation layer.
 10. The semiconductor light-receivingdevice according to claim 9, wherein the hydrogen concentration at leastin a part of the mesa structure is more preferably not more than 10% ofthe carrier concentration in the electric-field relaxation layer. 11.The semiconductor light-receiving device according to claim 9, whereinthe mesa structure is a III-V group semiconductor, and a p type impurityis at least one of a material selected from Be, Zn, Cd, Hg, Mg and C andan n type impurity is at least one of a material selected from Si, C, S,Se, Te and O.
 12. The semiconductor light-receiving device according toclaim 9, wherein the mesa structure is a III-V group semiconductor, anda p type impurity is at least one of a material selected from Be, Zn,Cd, Hg, Mg and C and an n type impurity is at least one of a materialselected from Si, C, S, Se, Te and O.
 13. The semiconductorlight-receiving device according to claim 9, wherein the avalanchemultiplication layer, the electric-field relaxation layer, and the lightabsorbing layer is formed over a semiconductor substrate in this order.14. The semiconductor light-receiving device according to claim 9,further comprising: a first cladding layer provided between theavalanche multiplication layer and the semiconductor substrate; and asecond cladding layer provided over the light absorbing layer.
 15. Thesemiconductor light-receiving device according to claim 14, wherein theSiN_(x) film or the SiO_(y)N_(z) film is formed over lateral faces ofthe first and second cladding layer.
 16. A manufacturing method of amesa semiconductor light-receiving device including a light absorbinglayer, an avalanche multiplication layer and an electric-fieldrelaxation layer over a semiconductor substrate, the method comprising:forming a mesa semiconductor structure; and forming a SiN_(x) film or aSiO_(y)N_(z) film using at least N₂ gas as a nitrogen source to alateral face of the mesa semiconductor structure.
 17. The manufacturingmethod of a semiconductor light-receiving device according to claim 16,wherein the SiN_(x) film is formed using SiH₄ gas in addition to N₂ gasand the SiO_(y)N_(z) film is formed using O₂ gas or N₂O gas in additionto N₂ gas and SiH₄ gas.
 18. The manufacturing method of thesemiconductor light-receiving device according to claim 16, wherein theSiN_(x) film or the SiO_(y)N_(z) film is manufactured by an ECR method.19. The manufacturing method of the semiconductor light-receiving deviceaccording to claim 17, wherein the SiN_(x) film or the SiO_(y)N_(z) filmis manufactured by an ECR method.
 20. A manufacturing method of a mesasemiconductor light-receiving device including a light absorbing layer,an avalanche multiplication layer and an electric-field relaxation layerover a semiconductor substrate, the method comprising: forming a mesasemiconductor structure; forming a SiN_(x) film or a SiO_(y)N_(z) filmto a side wall surface of the mesa semiconductor structure; andperforming a heat treatment in inert gas atmosphere at 450 degreesCelsius or more and 700 degrees Celsius or less.
 21. The manufacturingmethod of the semiconductor light-receiving device according to claim20, wherein the SiN_(x) film is formed using N₂ gas or NH₃ gas and SiH₄gas and the SiO_(y)N_(z) film is formed using N₂ gas or NH₃ gas and SiH₄gas and O₂ gas.